Hydraulically expansible drill bits



Sept. l5, 1967 A; w. KAMMERER, JR 3,339,547

HYDRAULICALLY EXPANSIBLE DRlLL BITS Filed Aug. 20, 1965 5 Sheets-Sheet lgk/'Gai agi fvwm/roe, REM/MERE@ Je,

rroemgx Sept. 5, 1967' A. w. KAMMERER, .1R 3,339,647

I HYDRAULICALLY EXPANSIBLE DRILL BITS v3 Sheets-Sheet 2 Filed lAug. 20,1965 fA/VENroe. I H20/E2 l. HHM/1452512, v7?.

A. w. KAMMERER, .1R 3,339,647

HYDRAULICALLY EXPANSIBLE DRILL BITS Sept. 5,` 1967 3 Sheets-Sheet 3Filed Aug. 2o, 1965 @It /M/ v ,l V .Il I l I III United States Patent3,339,647 HYDRAULICALLY EXPANSIBLE DRILL BITS Archer W. Kammerer, Jr.,Fullerton, Calif., assigner of one-fifth to Jean K. Lamphere, Fullerton,Calif., and three-fifths to Archer W. Kammerer, Fullerton, Calif.

Filed Aug. 20, 1965, Ser. No. 481,308 17 Claims. (Cl. 175-268) Thepresent invention relates to rotary drilling tools, and moreparticularly to drill bits of the expansible type capable of drilling orenlarging the diameters of well,

bores, severing casing and similar conduit strings disposed in wellbores, and milling away sections of casing, and the like, disposed inwell bores.

In certain rotary well drilling bits embodying expandable cutters, suchas drill bits of the type disclosed in United States Patent No.2,758,819, cutter expansion is effected hydraulically after the bit hasbeen lowered in the well bore to its desired operating location. Attimes, lthe lowering of the drill bit on a tubular string through theuid in the well bore causes inadvertent and undesirable prematureoutward expansion of the cutters, which can retard downward movement ofthe bit in the well bore, cause the bit to han-g up in the well bore,and which might produce some damage to the cutters and other parts ofthe bit.

It is an object of the .present invention to provide an expansiblerotary drill bit, in which the lluid in the well bore cannot effectinadvertent expansion of the bit cutters during lowering of the drillbit in the well bore.

Another object of the invention is to provide an expansible rotary drillbit having cutters expanded outwardly in response to the application offluid pressure to the bit, in which the iluid in the well bore cannotinadvertently expand the cutters of the bit during lowering of thelatter in the well bore.

A further object of the invention is to provide an expansible rotarydrill bit of the type disclosed in United States Patent No. 2,758,819,in which cutter expansion is elected by the relative upward movement ofa cutter carrying body along a mandrel, and in which the fluid in thewell bore is prevented from inadvertently elevating the body along themandrel during lowering of the drill bit in the well bore. In fact, thefluid in the well bore is utilized to urge and hold the body in itsposition downwardly of the mandrel during lowering of the bit in thewell bore.

This invention possesses many other advantages, and has other objectswhich may be made more clearly apparent from a consideration of severalforms in which it may be embodied. Such forms are shown in the drawingsaccompanying and forming part of the present speciiication. These formswill now be described in detail for the purpose of illustrating theIgeneral principles of the invention; but it is to be understood thatsuch detailed description is not to be taken in a limiting sense, sincethe scope of the invention is best defined by the appended` claims.

Referring to the drawings:

FIGURE 1 is a longitudinal section, with parts shown in elevation,through a drill bit embodying the invention,

with its cutters in retracted position;

FIG. 2 is a view similar to FIG. 1 illustrating the drill bit with itscutters in their expanded position;

FIG. 3 is an enlarged section through a portion of the drill bit, withthe parts in the position illustrated i1 FIG. 2;

FIG. 4 is a view similar to FIG. 3 illustrating ejection of an erodibletripping ball `through the apparatus;

FIG. 5 is a cross-section taken along the line 5-5 on FIG. 3;

ICC

FIG. 6 is a longitudinal section through a drill bit, with the cuttersin their initial retracted position, and illustrating another embodimentof the invention;

FIG. 7 is an enlarged section of a portion of the drill bit illustratedin FIG. 6;

FIG. 8 is a cross-section taken along the line 8--8 on FIG. 7;

FIG. 9 is a vertical section through another form of a portion of theapparatus illustrated in FIGS. 6 to 8, inclusive.

The invention is illustrated in the drawings as being applicable to arotary expansible drill bit A, secured to the lower end of a string ofdrill pipe B extending to the :top of a well bore C, and by means ofwhich the drill bit is lowered in the well bore to a desired locationtherein, where a hole enlarging, or other, operation is to commence. Theinvention is also rapplicable to other specic expansible rotary drillbits, such as those used for severing casing, and for milling away asection Ior length or" casing disposed in a well bore.

The upper portion of :the drill bit includes a mandrel 10 having anupper pi-n 11 threadedly connected to the lower end of the string ofdrill pipe B. This mandrel includes an upper kelly or drill stem member12 slidably splined to the main :body 13 of the drill bit. The exterior14 of the lower portion of the kelly 12 is non-circular in shape, beingtelescopically received in a companion noncircular bore 15 formed in themain bit body. As an example, the kelly exterior 14 and the socket 15may be of hexagonal shape to enable the kelly to be moved longitudinallywith respect to the body while still being capable of transmittingrotary movement to the body.

Y The mandrel 10 has a limited range of longitudinal movement within thebody, its downward movement being determined by engagement of the lowerend 16 of the kelly with an inwardly directed body shoulder 17, and itsrelative upward movement being limited by engagement of an externalshoulder or piston portion 18 of the kelly with a cylinder head 1'9secured to the -body 13'. The upper end of the head has a flange 20'engaging a body shoulder 21, the flange being prevented from movingupwardly of the body by split snap retainer rings 22 tting in the bodygroove 23 and overlying the flange. An annular guide 24 is releasablysecured to the body by a split snap ring 25 above the retainer ring.

The body 13 has a plurality of expansible parts mounted on it. Theseinclude cutter supporting members 26 pivotally mounted in body slots 27on hinge pins 28 suitably secured to the body to prevent their losstherefrom. Each cutter supporting member 26 depends .from its hinge pin28 and carries a cutter 29 at its lower end, specically disclosed asbeing of the toothed roller type, but which, if desired, may be of otherform, such as a drag, milling, or casing severing cutter.

The cutter supporting members 26 and the ,cutters 29 tend to occupy aretracted position substantially entirely within the confines of themain body 13 of the bit. These cutter supporting members and cutters areexpandable outwardly to enlarge the well bore to a diameter D andoperate upon a formation shoulder E between the enlarged well bore andthe smaller diameter well bore C therebelow. To accomplish theexpansion, each cutter supporting member has an inclined expandersurface 30 on its inner portion below the hinge pin which tapers in adownward and inward direction. Each expander surface terminates in alock surface 31 formed on a lock portion 32 of the cutter supportingmember 26. The outward expansion is accomplished by producing relativelongitudinal movement between the mandrel 10 and the bit body 13, whichwill produce relative longitudinal movement between the cuttersupporting members 26 `and a tubular member 33 that forms part of themain mandrel 1i). This tubular member includes a lower portion 34slidable within a guide bushing 35 mounted in a bridge 36 secured to thebody and extending across the body slots 27. This guide bushing isdisposed below the lo'ck portions 32 of the cutter supporting members.

Located initially substantially above the guide bushing 35, and belowthe hinge pins 28 and in cutter member recesses 37, is a mandrel lockand expander 38 adapted to engage the expander surfaces 30, and whichhas. outer surfaces 39 adapted to engage the lock surfaces 31. The lockand expander 38 may be formed integral with the tubular member 33, theupper end portion 40 of the latter being piloted withina socket 41formed in the lower portion of the kelly 12. The upper portion 40 is anenlarged boss on the tubular member, engaging a downwardly facingshoulder 42 of the kelly, the tubular member being held against thisshoulder by a suitable split retainer or lock ring 43 snapped into aninternal groove 44 encompassing the kelly socket and engaging the lowerend of the tubular member boss 40.

Drilling mud, or other fluid, can pass down through a central passage 45in the kelly or drill stem and into a central passage 46 extendingcompletely through the tubular member 33. Leakage of fluid around theexterior of the tubular member is prevented by a suitable side Seal ring47 mounted in the kelly and engaging the exterior surface of the boss40.

Assuming that the body 13 of the tool is elevated relatively along thetubular mandrel 10, the inclined expander surfaces 30 of the cuttersupporting members 26 are shifted upwardly along the lock and expanderportion 38 of the tubular member 33. During such upward shifting, thecutter supporting members 26 and the cutters 29 carried thereby will bepivoted about the hinge pins 28 and urged in an outward direction. Theupward movement of the body 13 with respect to the tubular mandrel cancontinue until the cutters 29 have been shifted outwardly to theirfullest extent, as determined by engagement of stop shoulders 48 on thecutter supporting members with companion shoulders 49 formed inthe bodyon opposite sides of the body slots 27. When such engagement occurs, thelower end 16 of the kelly portion 12 of the tubular mandrel engages thebody shoulder 17, and the lock and expander 38 on the tubular memberwill be disposed behind and in engagement with the lock portions 32 ofthe cutter supporting members, as disclosed in FIG. 2.

The relative longitudinal movement between the tubular mandral 10 andthe body 13 of the tool is accomplished hydraulically. Thus, the pistonor enlarged portion 18 on the drill stem 12 is received within acounterbore 50 formed in the upper portion of the tool body. This upperportion actually constitutes a cylinder 51 having a cylindrical wall 52extending from a lower shoulder 53, defining the bottom of thecounterbore, to and around the cylinder head 19.

A conned cylinder space 54 is formed between the piston portion 18 ofthe kelly, the periphery of the kelly above the piston 18, and thecylinder 51. A suitable packing or side seal ring 55 is mounted on thepiston for slidable sealing against the cylindrical wall 52 of thecylinder. Fluid is thereby prevented from passing in a downwarddirection between the piston 18 and cylinder 51. Similarly, fiuid isprevented from passing in an upward direction out of the annularcylinder space 54 by an inner side seal ring 56 in the cylinder head 19slidably and sealingly engaging the periphery of the kelly 12 above thepiston and also by an outer side seal ring 57 in the cylinder headsealingly engaging the cylinder wall S2.

When permitted to do so, fluid under pressure in the string of drillpipe B and in the tubular mandrel passa-ge 45 is fed into the cylinderspace 54 through one or more side ports 58 establishing communicationbetween the central passage 45 through the kelly and the cylinder space.As described hereinbelow, such uid under pressure is developed byrestricting the ow of uid through the passage 45 and through the tubularmember passage 46 of the mandrel, creating a back pressure in thepassage 45 which will be imposed Von the fluid in the cylinder space 54,and which will act upon the cylinder head 19 to urge the body 13 of thetool in an upward direction with respect to the tubular mandrel 10, forthe purpose of moving the cutter supporting members 26 along theexpander 38 and effecting outward expansion of the latter and of thecutters 29 carried thereby, in the manner described above.

In rotary expansible drill bits of the general type described above andin the above-identified patent, the lowering of the bit by means of thestring of drill pipe B through the drilling mud or other liquid in thewell bore C sometimes caused such liquid to shift or tend to shift thebody 13 of the tool relatively upwardly along the mandrel 10, causingthe cutter supporting members 26 to move upwardly along the mandrel lockand expander 38 and be urged in an outward direction. Such action isprevented in the embodiments of the invention illustrated in thedrawings. In fact, the fluid in the well bore externally of the drillbit A is caused to actually act in a downward direction on the body 13and retain it in its downward position relative to the mandrel 10, inwhich the cutter supporting members 26 and cutters 29 are in their fullyretracted positions, until cutter expansion is desired.

As disclosed in the Aform of invention illustrated in FIGS. l to 5,inclusive, the ports 58 through which Huid can flow between the centralmandrel passage 45 into the cylinder space 54 are closed initially by avalve sleeve 70 extending across them and releasably retained in suchposition by one or more shear screws 71 securing the valve sleeve to themandrel kelly 12. Leakage of uid around the exterior of the valve sleeve70 is prevented by upper and lower side seal rings 72 thereon onopposite sides of the ports 58 sealingly engaging the inner wall of themandrel passage 45. Upward movement of the valve sleeve in the mandrelis prevented by engagement of its upper end 73 with a downwardly facingmandrel or kelly shoulder 74.

The valve sleeve 70 carries a ow restricting member 75, such as a choke,secured within the Valve sleeve passage 76 and preferably made of anerosion resisting material, such as tungsten carbide. The upper portionof this choke or sleeve 75 has a cylindrical wall 77, the lower portion78 of the sleeve extending inwardly from opposite sides to provide anon-circular fluid passage portion 79 of restricted area, which area isto be further restricted by the subsequent engagement with the upwardlyfacing seat 80 that the inwardly `directed portion 78 of the sleeveprovides by an erodible valve element 81 to be pumped down through thedrill string B and into the drill bit A. This erodible valve element 81,which may be in the form of a ball made of mild steel, or other suitablematerial, subject to a relatively slow erosion under the action of fiuidacting thereon and owing therearound, engages the seat 80 atdiametrically opposite points, :as disclosed in FIGS. 2, 3 and 5, therebeing a space or an orifice passage 82 around the ball between the balland the sleeve seat 80 of relatively restricted area, through which thefluid can pass.

The drill bit A is lowered through the fluid in the well bore C by meansof the string of drill pipe B, the valve sleeve 70 being retained in itsport closing position, as illustrated in FIG. 1, which prevents uid inthe well bore, and `also from within the drill pipe and drill bit, frompassing through the ports 58 into the cylinder space 54, which willretain air `at substantially atmospheric pressure. During lowering ofthe drill bit through the drilling mud, or other fluid, in the wellbore, such fiuid acts on the bit body 13 and tends to elevate itrelatively along the mandrel 10, tending to effect outward expansion ofthe cutter supporting members 26 and cutters 29. In the present case,however, such upward movement tendency is prevented by the fact that thehydrostatic head of fluid is 4acting in a downward direction on thecylinder head 19, the force of such hydrostatic head of uid increasingas the drill bit is lowered to greater depths in the well bore andholding the body in the downward position -along the mandrel illustratedin FIG. l. The force can be quite substantial since the hydrostatic headof iuid externally of the apparatus is acting in a downward directionover the full cross-sectional -area of the cylinder head 19, and theonly resisting force acting in an upward direction on the cylinder headis air at atmospheric pressure trapped within the cylinder space 54.

During lowering of the drill bit in the well bore, fluid can passupwardly through the passage 46 through the tubular member 33 into thelower portion of the kelly 12, owing upwardly through the valve sleeve70 and the choke 75 into the kelly passage 45 thereabove, continuing oninto the drill pipe B to automatically fill the latter with lluid.

When the location in the well bore is reached at which the cutters 29are to be expanded outwardly, the erodible trip ball 81 is allowed togravitate down through the Huid in the drill pipe B, or is pumpeddownwardly therethrough, coming to rest upon the valve seat 80 formed bythe restricted portion of the choke. The iluid under pressure in thedrill pipe B and in the kelly passage 45 above the valve sleeve is thenincreased, some of the uid still being capable of passing around theball 81 for continued movement downwardly through the mandrel and intothe well bore below the lower end of the tubular member 33. A backpressure is built up in the kelly passage 45 above the sleeve 70 ofsuicient value as to overcome the shear strength of the screw or screws71 and disrupt the latter, the sleeve 70 then being shifted downwardlyto a position below the ports 58, the sleeve corning to rest upon theupper end of the tubular member 33 of the mandrel (FIGS. 2 to 4). It isprevented from moving back upwardly in the passage 45 to a positionacross the ports 58 by a retaining'device in the form of an expandablesplit snap ring 85 disposed in a groove 86 in the lower portion of thesleeve 70, and which expands outwardly into a groove 87 formed betweenthe kelly 12 and the upper end of the tubular member 33, the ring beingadapted to engage the upper side 88 of the groove and thereby preventingthe valve sleeve from returning to its upper position.

After the valve sleeve 70 has been shifted downwardly to its portopening position, as illustrated in FIG. 2, fluid under pressure,resulting from pumping drilling mud, or the like, downwardly through thedrill pipe B and through the mandrel 10, will build up a back pressurein the ported region of the kelly, due to the restriction to downwardflow of iluid around the ball 81 and through the choke 75, the uid underpressure passing through the ports 58 into the cylinder space 54 andacting in an upward direction to urge the body 13 upwardly of themandrel 10 and the cutter supporting members 26 upwardly along theexpander 38. During such downward pumping of fluid through the drillpipe and mandrel, the drill pipe and the drill bit are rotated to causethe cutters 29 to commence enlarging the well bore C. When the cuttershave been expanded outwardly to their fullest extent, the body 13 of thetool moves upwardly to bring its shoulder 17 into engagement with thelower end 16 of the kelly, at which time the expander and lock portion38 of the mandrel is disposed behind the lock surfaces 31 on the cuttersupporting members, as disclosed in FIG. 2.

After the cutters 29 have been expanded outwardly to their fullestextent, drilling fluid continues to be pumped down through the drillpipe B and out of the tool A for upward passage around the cutters inthe drilling region and through the annulus around the drill pipe B tothe top of the hole. The ball valve element 81, being erodible, willgradually be Worn away as fluid is pumped therearound. Under conditionsusually encountered in the well bore, substantial erosion of the ballvalve element will take place by the time the cutters have beenhydraulically expanded outwardly to their maximum outward position. Assuch erosion occurs, the orice area between the valve element 81 and thesleeve 75 increases, permitting greater quantities of lluid to be pumpedfrom the mandrel 10 into the well bore. Eventually, erosion of the valveelement 81 will occur to such an extent that it is forced completelythrough the lower uid passage portion 79 of the sleeve 75 and into thetubular member passage 46, being ejected through the lower end of thelatter into the well bore.

The hole enlarging operation can continue with the appropriate amount ofdrilling weight being imposed upon the cutters 29. Such downwarddrilling weight will retain the mandrel lock 38 behind the cuttersupporting members 26 to prevent inadvertent inward shifting of thecutters from their full outward expanded position.

When the drill bit is to be removed from the well bore, the pumping offluid downwardly through the drill lpipe and through the tool isdiscontinued and the drill pipe B elevated, which will raise the mandrel10 within the body 13 of the tool back to the position illustrated inFIG. 1. This will allow the cutters 29 to shift inwardly to theirinitial retracted position and allow the tool to be elevated in the wellbore and removed completely therefrom.

In the form of invention illustrated in FIGS. 6, 7 and 8, the body 13 ofthe drill bit is prevented from shifting inadvertently upwardly alongthe mandrel 10 by preventing lluid under pressure from entering thecylinder space 54 during lowering of the tool through the drilling mud,or other lluid, in the well bore C. As disclosed, a choke orifice 75a iswelded, or otherwise suitably mounted, within the lower end of thetubular member 33. This choke orifice may have the same shape as the one75 illustrated in the other embodiment of the invention, and the samenon-circular passage 79a through its lower portion. It is closedinitially by a plug having an upper portion 91 shaped to conform to theshape of the noncircular opening 79a through the choke, and which has anoutwardly extending tiange 92 adapted to engage the lower' end of thechoke or tubular sleeve 75a. The portions 91, 92 of the plug are made ofa suitable elastomer material, such as rubber, so that its ange 92yseals against the lower end of the sleeve 75a. A metal disc 93 ismolded to the lower end of the elastomer plug, which has a lowerextension 94 projecting through a central hole 95 in the metal disc.

The plug is mounted within the carbide sleeve 75a, as disclosed in FIGS.6, 7 and 8, to close the passages 46, 45 through the mandrel 10 againstupward flow of iiuid thereinto. During lowering of the drill pipe B anddrill bit A through the drilling mud, or other uid, in the well bore,such-Huid cannot pass upwardly into the mandrel passage for the purposeof filling the latter and the drill pipe B. Accordingly, the cylinderspace 54 will contain air at atmospheric pressure only. As the drill bitmoves downwardly through the fluid in the Well bore, the latter cannotshift the .body 13 upwardly with respect to the mandrel 10, 'since thehydrostatic head of iluid is acting downwardly on the body over the areaof its cylinder head 19 and will hold the body 13 in its full downwardposition along the mandrel, in the same manner as described above inconnection with the form of invention disclosed in FIGS. 1 to 5,inclusive.

When the location in the well bore is reached at which the cutters 29are to Ibe expanded, the drill pipe B and mandrel passage 45, 46 arelled with drilling mud, or the like, from the top of the well bore,whereupon the erodible ball 81 is placed in the drill pipe and is pumpeddownwardly therethrough. The initial pumping action will blow the plug90 out of the choke orice 79, whereupon the fluid can pass out of thelower end of the mandrel 10 into the Well bore. When the ball 81 reachesits `seat 80a in the choke orifice, fluid pressure can be built up inthe mandrel and in the cylinder space 54 for the purpose of elevatingthe body 13 along the mandrel 10 while the drill pipe B and drill bit Aare being rotated to effect cutter expansion and enlargement of the wellbore, in the manner described above in connection with the other form ofthe invention. During the cutting action on the formation, some fluidcan pass around the ball 81 and into the well bore so as to carry thecuttings upwardly around the bit and drill pipe to the top of the hole.The erosion of the ball 81 will reduce its size to the extent at whichit will be pumped out through the choke orifice 75a into the well bore,after which a larger volume of drilling mud can be pumped through theapparatus during operation of the drill bit in enlarging the well bore.

In lieu of the solid elastomer plug, illustrated in FIGS. 6, 7 and 8, asimilarly shaped plug 90a, but one having a small diameter passage 96therethrough, can be used and inserted in the choke orifice 75a in thesame manner as illustrated in FIGS. 6 and 7. The small diameter passage96 will allow the fluid in the well bore to flow into the mandrelpassage 46, 45 at a restricted rate during lowering of the drill bit Ain the well bore. However, during such lowering, the hydrostatic head offluid in the drill pipe will be substantially less than that surroundingthe drill pipe B, which will still provide a hydrostatic headdifferential externally of the drill pipe acting in a downward directionon the body 13 over the area of the annular cylinder head 19, holdingthe body in its downward direction. Each time downward movement of thedrill pipe B and bit A is arrested, the fluid in the well .bore cancontinue to pass upwardly through the hole or passage 96 in the plug tocontinue filling the drill pipe with fluid.

When the location in the well bore is reached at which the cutters 29are to be expanded, the drill pipe is allowed to fill with fluid in thewell bore flowing through the plug hole 96, or filling of the drill pipecan be completed from the top of the well bore by pumping fluidthereinto. In any event, the trip yball 81 can be placed Within thedrill pipe B and pumped downwardly therethrough, the plug 90a beingblown out of the choke and the ball coming to rest upon its seat 80a,whereupon fluid pressure can be built up in the drill pipe, mandrelpassage and cylinder space for the purpose of hydraulically elevatingthe body 13 along the mandrel 10, while the drill pipe and bit arerotated, to effect cutter expansion. The erodible ball 81, as before,will reduce in diameter and will be ejected from the choke passage 79.

The plug 90a illustrated in FIG. 9 may be used when the drill bit is tobe lowered to relatively deep locations in the well bore, which willintroduce comparatively high external hydrostatic pressures acting in adownward direction on the body 13 of the tool and tending to keep itdownwardly along the mandrel 10. The fluid in the well bore flowingthrough the plug passage 96 will cause the drill pipe to fill partiallywith fluid and decrease the hydrostatic head differential actingdownwardly on the body of the drill bit. For that matter, when the solidplug illustrated in FIGS. 6 to 8 is used, the drill pipe could bepartially filled with drilling mud, or the like, from the top of thewell bore to prevent the hydrostatic head differential acting downwardlyon the bit body from becoming too great.

I claim:

1. In a rotary drill bit to be lowered through fluid in a well bore on adrill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expani sion laterally outwardly thereof; fluid actuated meansresponsive to the pressure of fluid in said passage for expanding saidcutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion of said cutter means by said fluidactuated means;

means for maintaining fluid pressure within the drill bit, and acting onsaid fluid actuated means, at a substantial lower value than theexternal hydrostatic head of fluid acting on said fluid actuated meansduring lowering of the drill bit in the well bore to prevent expansionof said cutter means; and means for rendering said maintaining meansineffective to permit said cutter means to be expanded by said fluidactuated means.

2. In a rotary drill bit to be lowered through fluid in a well bore on adrill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; fluid actuated meansresponsive to the pressure of fluid in 'said passage for expanding saidcutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion of said cutter means by said fluidactuated means; means for restricting upward flow of fluid in saidpassage to said fluid actuated means during lowering of the drill bit inthe well bore to prevent expansion of said cutter means; and means forrendering said restricting means ineffective to permit said cutter meansto be expanded by said fluid actuated means.

3. In a rotary drill bit to be lowered through fluid in a well bore on-a drill string: a body structure having a passage through whichdrilling fluid is adapted to flow; cutter means mounted on said bodystructure for expansion laterally outwardly thereof; fluid actuatedmeans responsive to the pressure of fluid in said passage for expandingsaid cutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion of said cutter means 'by 'said fluidactuated means; means for restricting flow of fluid in said passage tosaid fluid actuated means during lowering of the drill bit in the Wellbore to prevent expansion of said cutter means; and means for renderingsaid restricting means ineffective to permit said cutter means to beexpanded by said fluid actuated means.

4. In -a rotary drill bit to be lowered through fluid in a well bore ona drill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; fluid actuated meansresponsive to the pressure of fluid in said passage for expanding saidcutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion of said cutter means by said fluidactuated means; means for restricting flow of fluid in the well boreupwardly into said passage during lowering of the drill bit in the wellbore to prevent expansion of said cutter means; and means for renderingsaid restricting means ineffective to permit said cutter means to beexpanded by said fluid actuated lmeans.

5. In a rotary drill bit to be lowered through fluid in a well bore on adrill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; fluid actuated meansresponsive to the pressure of fluid in said passage for expanding saidcutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion of said cutter means by said fluidactuated means; and passage closure means restricting the flow of wellbore fluid upwardly in said passage during lowering of the drill bit inthe well bore to prevent expansion of said cutter means, said closuremeans being removable from closed relation to said passage by fluidpressure in said passage thereabove.

6.` In a rotary drill -bit to be lowered through fluid in a well bore ona drill string: a 'body structure having a passage through whichdrilling fluid is adapted to flow;

cutter means mounted on said body structure for expansion laterallyoutwardly thereof; fluid actuated means responsive to the pressure offluid in said passage for expanding said cutter means, said fluidactuated means being responsive to the hydrostatic head of fluid in thewell bore externally of the drill bit which tends to resist expansion ofsaid cutter means by said fluid actuated means; and passage closuremeans restricting the flow of well bore fluid upwardly in said passageduring lowering of the drill bit in the well bore to prevent expansionof said cutter means, said closure means being removable from closedrelation to said passage by fluid pressure in said passage therea'bove,said closure means having a choke orifice therethrough to permit wellbore fluid to flow upwardly therethrough at a restricted rate into saidpassage.

7. In a rotary drill bit to be lowered through fluid in a well bore on adrill string: a body structure having a passage through-which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; fluid actuated meansresponsive to the pressure of fluid in said passage for expanding saidcutter means, said fluid actuated means being responsive to thehydrostatic head of fluid in the well bore externally of the drill bitwhich tends to resist expansion `of said cutter means by said fluidactuated means; valve means in said body structure initially preventingflow of fluid from said passage to said fluid actuated means; and meansfor shifting said valve means to a position permitting flow of fluidfrom said passage to said fluid actuated means.

8. In a rotary drill bit to be lowered through fluid in a well bore on adrill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; fluid actuated means on saidbody structure for expanding said cutter means; said body structurehaving port means communicating said passage with said fluid actuatedmeans; said fluid actuated means being responsive to the hydrostatichead of fluid in the well bore externally of the drill bit which tendsto resist expansion of said cutter means by said fluid actuated means; avalve sleeve in said passage initially closing said port means; andmeans for shifting said valve sleeve to port lopening position.

9. In a rotary well drilling bit to be lowered through fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mandrel having apassage through which the drilling fluid is adapted to flow;coengageable expander means on said mandrel and cutter means;hydraulically movable means on said body subject to the pressure offluid in said passage for elevating said body and cutter means withrespect to said mandrel to cause said expander means to expand saidcutter means laterally outward; said hydraulically movable means beingresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends to resist elevation of said body and cuttermeans with respect to said mandrel; means for maintaining fluid pressurewithin said passage and acting on said hydraulically movable means at asubstantially lower value than the external hydrostatic head of fluidacting on said hydraulically movable means during lowering of the drillbit in the well bore to prevent elevation of said body and cutter meanswith respect to said mandrel; and means for rendering said maintainingmeans ineffective to permit fluid pressure in said passage to elevatesaid body and cutter means with respect to said mandrel.

10. In a rotary drill bit to be lowered through fluid in a well bore ona drill string: a body structure having a passage through which drillingfluid is adapted to flow; cutter means mounted on said body structurefor expansion laterally outwardly thereof; actuating means on said bodystructure for expanding said cutter means, said actuating means beingresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends to resist expansion of said cutter means bysaid actuating means; means for maintaining fluid pressure Within thedrill bit and acting on said actuating means at a substantially lowervalue lthan the external hydrostatic head of fluid acting on saidactuating means during lowering of the drill bit in the well bore toprevent expansion of said cutter means; and means for rendering saidmaintaining means ineffective to permit said cutter means to be expandedby said actuating means.

411. In a rotary well drilling bit to be lowered through fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mandrel having apassage through which the drilling fluid is adapted to flow;coengageable expander mean-s on said mandrel and cutter means;hydraulically cmovable means on said body subject to the pressure offluid in said passage for elevating said body and cutter means withrespect to said mandrel to cause said expander means to expand saidcutter means laterally outward; said hydraulically movable means beingresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends I to resist elevation of said body andcutter means with respect to said mandrel; means for restricting upwardflow of fluid in said passage to said hydraulically movable means duringlowering of the drill bit in the well bore -to prevent elevation of saidbody and cutter means with respect lto said mandrel; and means forrendering said restricting means ineffective to permit upward movementof said body and cutter means with respect to said mandrel in responseto fluid pressure in said passage.

12. In a rotary well drilling bit to be lowered through fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mand-rel having apassage through which the drilling fluid is adapted i to flow;coengageable expander means on said mandrel and cuttermeans;hydraulically movable means on said body subject to the pressure offluid in said passage for elevating said body and cutter means withrespect to said mandrel to cause said expande-r means to expand saidcutter means laterally outward; said hydraulically movable means beingresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends to resist elevation of said body and cuttermeans with respect to said mandrel; means for restricting flow of fluidin the well bore upwardly into said passage during lowering of the drillbit in the well bore to prevent elevation of said body and cutter meanswith respect to said mandrel; and means for rendering said restrictingmeans ineffective to permit elevation of said .body and cutter meanswith respect to said mandrel in response to fluid pressure in saidpassage.

13. In a rotary well drilling bit .to be lowered through fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mandrel having apassage ythrough which the drilling fluid is adapted to flow;coengageable expander means on said mandrel and cutter means;hydraulically movable means on said body subject to the pressure offluid in said passage for elevating said body and cutter means withyrespect to said mandrel to cause said expander means to expand saidcut-ter means laterally outward; said hydraulically movable means beingresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends to resist elevation of said body and cuttermeans with respect to said mandrel; and closure means for said passagerestricting the flow of well bore uid upwardly in said passage duringlowering of the drill bit in the well bore to prevent elevation of saidbody and cutter means with respect to said mandrel, said closure meansbeing removable from closed relation to said passage by fluid pressurein said passage thereabove.

14. In a rotary well drilling bit to be lowered through fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mandrel having apassage through which the drilling fluid is adapted to flow;coengageable expander means on said mandrel and cutter means;hydraulically movable means on said body subject to the pressure offluid in said passage for elevating said body and cutter means withrespect to said mandrel to cause said expander means to expand saidcutter means laterally outward; said hydraulically movable means bein-gresponsive to the hydrostatic head of fluid in the well bore externallyof the drill bit which tends to resist elevation of said body and cuttermeans with respect to said mandrel; and plug means in said passagerestricting the flow of well bore uid upwardly in said passage duringlowering of the drill bit in the well bore to prevent elevation of saidbody and cutter means with respect to said mandrel, said plug meansbeing ejectable from said passage by fluid pressure in said passa-gethereabove, said plug means having a choke orice to permit well borefluid to flow upwardly therethrough at a restricted rate into saidpassage.

15. In a rotary well drilling bit to be lowered throu-gh fluid in a wellbore on a drill string: a body; cutter means mounted on said body forexpansion laterally outwardly thereof; a mandrel connectible to a drillstring and slidably splined to said body, whereby drilling torque istransmitted from said mandrel to said body, said mandrel having apassage through which the drilling fluid is adapted to flow;coengageable expander means on said mandrel and cutter means;hydraulically movable means on said body subject to the pressure of uidin said passage or elevating said body and cutter means with respect tosaid mandrel to cause said expander means to expand said cutter meanslaterally outward; said hydraulically movable means being responsive tothe hydrostatic head of tluid in the well bore externally of the drillbit which tends to resist elevation of said body and cutter means withrespect to said mandrel; valve means in said passage initiallypreventing ilow of fluid from said passage to said hydraulically movablemeans; and means for shifting said valve means to a position permittingilow of lluid from said passage to said hydraulically movable means.

16. In a rotary drill bit to be lowered through fluid in a well bore ona drill string: a body; cutter means mounted on said body for expansionlaterally of said body; a mandrel connectible to a drill string andslidably splined to said body, whereby drilling torque is transmittedfrom said mandrel to said body; coengageable expander means on saidmandrel and cutter means; said mandrel having a passage through whichdrilling tluid is adapted to flow; hydraulically movable means on saidbody; port means in said mandrel establishing communication between saidpassage and hydraulically movable means, whereby fluid pressure in saidpassage can ow through said port to said hydraulically movable means toelevate said body and cutter means with respect to said mandrel to causesaid expander means to expand said cutter means laterally outward; saidhydraulically movable means being responsive to the hydrostatic head offluid in the well bore externally of the drill bit which tends to resistelevation of said body and cutter means with respect to said mandrel; avalve sleeve in said passage initially closing said port means; andmeans for shifting said valve sleeve to port opening position` 17. In arotary drill bit to be lowered through fluid in a well bore on a drillstring: a body; cutter means mounted on said body for expansionlaterally of said body; a mandrel connectible to a drill string andslidably splined to said body, whereby drilling torque is transmittedfrom said mandrel to said body; coengageable expander means on saidmandrel and cutter means; said mandrel having a passage through whichdrilling uid is adapted to flow; hydraulically movable means on saidbody; port means in said mandrel establishing communications betweensaid passage and hydraulically movable means, whereby fluid pressure insaid passage can ow through said port to said hydraulically movablemeans to elevate said body and cutter means with respect to said mandrelto cause said expander means to expand said cutter means laterallyoutward; said hydraulically movable means being responsive tothehydrostatic head of uid in the well bore externally of the drill bitwhich tends to resist elevation of said body and cutter means withrespect to said mandrel; a valve sleeve in said passage initiallyclosing said port means, said valve sleeve having a seat therein; and anerodible member movable downwardly in said passage into engagement withsaid seat to provide an orice to choke the ilow of fluid in said passageand cause a back pressure to be built up in said passage for shiftingsaid valve sleeve to port opening position, said erodible 4memberwearing away as fluid is pumped through said passage to substantiallyenlarge said orice.

References Cited UNITED STATES PATENTS 7/1957 Kammerer 175-268 7/1965Kammerer 175-267

1. IN A ROTARY DRILL BIT TO BE LOWERED THROUGH FLUID IN A WELL BORE ON ADRILL STRING: A BODY STRUCTURE HAVING A PASSAGE THROUGH WHICH DRILLINGFLUID IS ADAPTED TO FLOW; CUTTER MEANS MOUNTED ON SAID BODY STRUCTUREFOR EXPANSION LATERALLY OUTWARDLY THEREOF; FLUID ACTUATED MEANSRESPONSIVE TO THE PRESSURE OF FLUID IN SAID PASSAGE FOR EXPANDING SAIDCUTTER MEANS, SAID FLUID ACTUATED MEANS BEING RESPONSIVE TO THEHYDROSTATIC HEAD OF FLUID IN THE WELL BORE EXTERNALLY FOR THE DRILL BITWHICH TENDS TO RESIST EXPANSION OF SAID CUTTER MEANS BY SAID FLUIDACTUATED MEANS; MEANS FOR MAINTAINING FLUID PRESSURE WITHIN THE DRILLBIT, AND ACTING ON SAID FLUID ACTUATED MEANS, AT A SUBSTANTIAL LOWERVALUE THAN THE EXTERNAL HYDROSTATIC HEAD OF FLUID ACTING ON SAID FLUIDACTUATED MEANS DURING LOWERING OF THE DRILL BIT IN THE WELL BORE TOPREVENT EXPANSION OF SAID CUTTER MEANS; AND MEANS FOR RENDERING SAIDMAINTAINING MEANS INEFFECTIVE TO PERMIT SAID CUTTER MEANS TO BE EXPANDEDBY SAID FLUID ACTUATED MEANS.